Strawberry Plants & Aphids

by Alice Moon

Aphids rarely achieve numbers that cause damage in California, and not every area experiences aphid infestations great enough to justify intervention and treatment. Aphids are generally more problematic in the spring and fall and under dusty conditions. Most aphid damage occurs when temperatures warm to a range of 65 to 80 degrees Fahrenheit. Locations where moderate temperatures and high humidity occur together see greater infestations. Sunset’s Climate Zones 14 and 17 have humid conditions that could lead to increased aphid numbers.

Numbers

Aphids can become a problem in zones that experience mild conditions because the insects are able to reproduce for a longer period, sometimes all year. Aphids have the ability to produce live young and to do so asexually, without the need for a mate. Aphids can produce up to 12 nymphs a day, and each of those nymphs can start reproducing within a week. In some areas, high summer heat kills the pests before they achieve large numbers. In coastal areas, growers may experience more issues with aphids; however, in some humid areas, fungal diseases kill large numbers of aphids, giving growers a helping hand.

Types

Aphids are pale, pear-shaped insects with soft bodies. They are 1/10 inch long and have two tube-shaped cornicles protruding from their back ends. Aphids may have wings or appear wingless. Several types may be found on strawberry plants: Strawberry aphids and green peach aphids are green or yellow. Potato aphids are pink or green. Melon aphids are yellowish green to greenish black. While you typically find slow-moving aphids by looking on the undersides of plants’ leaves, the part of the plant targeted sometimes depends on the species of aphid involved. For example, green peach aphids tend to prefer young strawberry plants, while melon aphids congregate on stems when they infest strawberry patches.

Damage

In sufficient numbers, aphids can cause several forms of damage, including stunted shoots, curled and yellow leaves, distorted plants and the formation of galls. Aphids may also pass viruses to your strawberry plants. As they feed, aphids produce a sticky substance called honeydew. Sooty mold grows on honeydew, harming the appearance of your plants and fruits but not causing them serious damage.

Treatment

Check your plants often, and act quickly when aphids are found. Damaged plants make it easier for the pests to evade detection. You may see a greater number of ants or insect predators that feed on aphids if your plants are infested. These beneficial insects may be killed by applications of pesticides. The University of California’s Integrated Pest Management Program recommends insecticidal soap to treat strawberry plants, because it has the least impact on beneficial insects. Treat when aphid numbers reach an average of 10 per leaf. For smaller numbers of aphids, spray the pests away with a stream of water.

Prevention

Do not apply more nitrogen than recommended for your specific soil and conditions. Nitrogen not only drives excess foliage growth but also favors aphid reproduction. Plant and maintain habitats that support beneficial insects. Treat other plants growing near your strawberries if they are hosting aphids. Plant strawberry varieties resistant to viruses transmitted by aphids if you plan to keep your plants for several years.

About the Author

Alice Moon is a freelance writer with more than 10 years of experience. She was chosen as a Smithsonian Institute intern, working for the National Zoo in Washington, D.C., and has traveled throughout Asia. Moon holds a Bachelor of Science in political science from Ball State University.

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